(1) Field of the Invention
The present invention relates to an improvement in the water collecting and distributing apparatus disposed in a lower portion of a high speed filter basin.
(2) Description of the Prior Art
FIG. 1 of the accompanying drawing shows a conventional apparatus for collecting and distributing water, disposed in a lower portion of a high speed filter basin. The lower portion of the water collecting and distributing apparatus is constructed by a filter medium or filter layer 2, a gravel layer 3 and hollow blocks 4 arranged below these layers 2 and 3. Each block 4 has a number of holes in the top wall thereof. Reference numeral 5 represents a dam for collecting filtrate or clarified water, the numeral 6 represents a conduit for distributing back wash water for washing away suspended substance, colloidal substance and solids adhering to the filter medium 2, and the reference numeral 7 represents a trough for supplying raw water containing suspended substance, colloidal substance and solids to be removed by filtration. In this conventional water collecting and distributing apparatus for a filter basin, while raw water or dirty water supplied to the filter basin passes through the filter medium 2 and gravel layer 3, suspended substances, colloidal substances and solids contained in the raw water or dirty water adhere to the filter medium 2 and are thus removed from the water, and the filtrate is collected from holes formed in the top walls of the blocks 4 through the interior of the blocks 4, discharged to the outside of the basin and applied to an appropriate use. If the filtration is conducted continuously for a certain length of time, solids and other substances become deposited and accumulated in the filter medium 2 to reduce the filtration capacity. In order to restore the original filtration efficiency, the filter medium 2 is washed by flowing water from the water distributing conduit 6 to the gravel layer 3 and the filter medium 2 through the interiors and top wall holes of the blocks 4 in a direction reverse to the water-flowing direction in the filtration operation. With the conventional apparatus under consideration, it certainly is feasible to collect the clarified water or filtrate and to distribute wash water for cleansing the filter media. However, it is inoperable in cleansing the filter medium to send air from inside the block 4 through holes in the upper wall thereof and the filter medium and thereby have the solids or the like attached or accumulated onto the filter medium floated with bubbles of the air or contacted with the air to undergo oxidation. To carry out such scouring with air, unavoidable is to provide an air supply piping and accordingly an increase in the cost of construction of the apparatus. If air pipes are formed by using a metallic material, they are corroded or massive rusts are formed, and therefore, the pipes are readily damaged or clogged. If air pipes are formed by using a concrete material or the like, they are readily made brittle or worn away. Accordingly, when air pipes of a metallic material or concrete are disposed separately, it is difficult to operate the water collecting and distributing apparatus stably for a long time.